1. Field of the Invention
The present invention relates to transparent polyamide moulding materials containing cycloolefin copolymers and the use thereof.
2. Discussion of Background Information
Polyamide moulding materials containing cycloolefin copolymers are known from patent specification DD 203 060 A. Thermoplastic combinations based on norbornene/ethylene copolymers and polyamides having approximately equal quantitative proportions of the two polymers are described there. As suitable polyamides mention is made of aliphatic polyamides, polyamides having cycloaliphatic chain building blocks, aliphatic-aromatic polyamides and/or aromatic polyamides, usually with specific compounds as an example. Transparency is not one of the requirements for the polyamide moulding materials described. The optical properties of those polyamide moulding materials are not disclosed.
JP 2011-057864 A discloses moulding materials which are based on cycloolefin copolymers as the main component and which contain a smaller quantity of an added aliphatic polyamide in relation thereto. The cycloolefin copolymers claimed there have a glass transition temperature Tg from 50° C. up to a maximum of 100° C. Aliphatic polyamides having a fraction of at least 50 mol % lactamic or aminocarboxylic acid units are used. The transparency of these compositions is only low since merely a visual contact transparency is given.
In the brochure “TOPAS Cycloolefin Copolymer (COC)” of the COC manufacturer TOPAS Advanced Polymers, May 2007 edition, cycloolefin copolymers are described more accurately as a copolymerization product of the bicyclic olefin norbornene and ethylene. The good compatibility of COC with polyolefins to produce blends is mentioned and it is explicitly pointed out that the addition of foreign also transparent thermoplastics to COC leads to severe opacity. The designation TOPAS is a registered trademark.
Compared with other thermoplastics, polyamides have the particular feature that according to the type, they can absorb a certain quantity of water from the ambient moisture, with the result that the volume or the dimensions of moulded parts or coatings fabricated therefrom or certain mechanical properties of the moulded parts or coatings fabricated therefrom can vary. This also applies to transparent polyamides.
In order to achieve a good dimensional stability and more constant mechanical properties it is desirable to keep the water absorption of a polyamide moulding material low. To this end, the polyamide can, for example, be mixed with other components. In the case of transparent polyamides however, these components usually have a negative influence on the optical properties, i.e. the light transmission and the haze (opacity) of the resulting polyamide moulding material.